Firstly:
Content Fragment - Is of type dam:asset having data without experience.
Experience Fragment - Is of type cq:Page , which will have data and experience.
Any Data stored is content fragment can be exposed as a content service using various ways
Option1: Write custom code , which will return the data to external application in json or xml format.
Pros: Full control on the contract. Any updates to the content fragment model like adding a new field etc will not impact the contract.
Con : Developing a code example using servlet.
Option2 : Use the OOTB new AEM HTTP API
Con: No control on the contract. Any new field additions will impact contract.
Option2: is suggestible for simple integrations.
Option1 : suggestible for complex integrations.
content fragment exposing vis experience fragment --> feel like invalid.